Here are some from me:

I don’t like the ages in canon at all. I put Anakin as a 10 year old in TPM, Padmé 14 and Obi-Wan 25. Them saying in AOTC that “haven’t seen her in 10 years” and all those references to 10 years are just a way to round it, when in fact 11 years passed between TPM and AOTC (every year counts, trust me!). That puts Anakin at 21 and Padmé at 25, Obi-Wan at 36 in AOTC.
As a folow-up, the Clone Wars lasted for seven years. Several parts of the ROTS novelization are canon to me here, especially the ones about Obi-Wan and Anakin’s relationship - “The war made them one. There is no Obi-Wan without Anakin” and stuff like that. The war made Anakin deeply paranoid especially about his relationship to Padmé, and every time they meet is like in ROTS or the 2D Tartakovsky show - something really desperate and sort of hidden, not knowing when the next time will be.
All of this adds up meaning that by ROTS, Anakin is 28, Padmé 32 and Obi-Wan 43.
Anakin barely gets any sleep during ROTS, and doesn’t really eat. He’s going completely on auto-pilot, like he’s numb. Nothing feels real to him. It’s all a dream, or a nightmare.
23 years pass between ROTS and the original Star Wars, meaning ROTS takes place in 23 BBY. Kenobi takes place in 13 BBY, Solo takes place in 8 BBY, and Rebels doesn’t end on the same year Star Wars takes place.
Luke and Leia are 23 in Star Wars, Ben is 66, Vader is 51, Han is 31.
In Star Wars, the Death Star was mostly empty, and the only pilots it had available are the ones sent to fight the Rebel spaceships. That’s because the Empire desperately wanted it out there doing work, even when they really should’ve waited more months to arm it up and have its full capablities of personnel filled.
3 years pass between Star Wars and Empire. A lot happened in those three years.
For Luke, he studied more and more of the Force, but was very much not a patient and calm kid. The disturbance in the Force felt by Vader and the Emperor in Empire is Luke finally being able to make the Force “obey one of his commands”, as opposed to only “controlling his actions” as it had done up to that point. That was when he managed to be calm, at peace, in focus and grab the lightsaber in the Wampa cave, which really made him go that extra step in his connection to the Force and made him atuned enough with it in order for Ben to appear before him, who sent him to Dagobah in the next step of his journey. All of that combined means there’s a new player in town.
In those three years, Leia and Han hooked up several times but nothing ever came out of it. It’s why Han is so sure of his advances in Empire, and it really takes all of the predatory nature of the relationship out of the equation if something already happened between them.
Time passes differently in Dagobah, but not because of any sci-fi reason, but because of the Force. Han and Leia’s adventure in Empire lasts for a couple weeks, while Luke spends months in Dagobah.
Finally, two years pass between Empire and Jedi. Vader dies aged 56, Luke and Leia are 28, Han is 36.
The Force is something that if you have enough outside guidance you can mostly improve at it yourself. Luke is essentially a self-taught Jedi, and he spent the two years between Empire and Jedi honing his skills and enhancing his connection to the Force, working his ways around problems he knew existed from his time with Yoda.

As for more general stuff:

Force potential can’t be passed down by blood. The Skywalker family is strong in particular because they’re a family that “shouldn’t even exist.” It’s the result of the Force itself acting and trying to course correct the state of the Galaxy. Anakin fails and it falls upon his children, who are indeed the two “chosen ones”, if there’s such a thing.
I like to think the PT Jedi misinterpreted the Chosen One prophecy with Anakin and it’s what caused theirs and his doom, and that the PT is more of a subversion of that trope à la Matrix than actually just the trope.
The Force isn’t like Harry Potter magic, meaning, you can’t “use it by accident just because you have it”, like Ezra does all the time for instance. It’s my main issue with Rebels. That’s not how the Force works. Like Ben says, the Force controls your actions like it does for Luke in the first film (but even that takes effort! Neither Luke nor Anakin ever use it “by accident”), but you have to work hard and study a ton to have control over it and be one with it. It’s like mastering a martial art, or an instrument, or any skill like that. Gotta devote yourself and really be passionate.
This is something Pablo Hidalgo actually mentioned on twitter yesterday: Darth Vader wasn’t very well known before the original film, after which Death Squadron (Vader’s fleet) is formed to personally hunt down the Alliance after there’s a person of interest (Luke) with them. The reactions from Motti/Ozzel/Jerjerrod are a good indication of Vader’s reputation within the Empire and out by the time of each film.
The back to back hit Scarif/Yavin is what made the Rebellion really grow in size and the Empire take them seriously.

JEDIT: Among some little fixes here and there to this, I’d like to add that I’ve personally added several headcanons from this thread into mine. For instance, the one about the Death Star II really being a shell that can’t even blow up planets and simply exists for political reasons (I’d arrived at it only existing for political reasons, but the stuff about it barely being a Death Star makes so much sense it’s almost obvious, thanks!), or the one about Anakin’s final moment being seeing Padmé in Luke. There was also mention of Bail and Breha’s final moments be mourning Leia since Tarkin had signed her termination - really dark stuff that you don’t even consider watching the original film. Talk about extra material making things more important…